ESTIMATION OF HORIZONTAL STRESSES AT DEPTH IN FAULTED REGIONS AND THEIR RELATIONSHIP TO PORE PRESSURE VARIATIONS

This paper focuses on the relationships used for estimating the magnit udes of horizontal stresses acting in faulted sedimentary basins. Rela tionships are derived here based on the assumptions of a faulted but e ssentially elastic rock and take into account the tectonic stress comp onent associated with active normal and thrust faults, as well as the pore pressure. The equations presented predict that the orientation of the minimum stress can change once a normal or thrust fault has forme d. They further predict that an increase in pore pressure gradient wil l result in a more isotropic stress state. Field data are used to asse ss the predictions and include stress-depletion measurements from norm ally faulted basins and stress measurements performed ''at depth'' in compressive tectonic ''thrust'' regions.